The present invention generally concerns an improved variable speed drive and more particularly concerns an improved, maintenance friendly mechanical adjustable variable speed belt drive and related methods.
One type of widely used mechanical adjustable drive is referred to generally as a variable speed belt drive, and includes a V-belt entrained about two pairs of relatively axially movable discs received on respective input and output shafts. In order to change the drive ratio between the two shafts, various mechanisms are used to change the spacing between discs of a respective pair and to otherwise cause the position of the V-belt to change relative the disc pairs and relative the two shafts. As is well known to those of ordinary skill in the art, such a type of variable speed belt drive permits constant speed input power applied to the input shaft to be changed into a controlled, i.e., selected, variable speed drive output at the output shaft.
It is quite common that most components of such prior art variable speed belt drives are protectively enclosed, such as in a housing or casing. Frequently the input shaft is mated with the drive shaft of a constant speed electric motor or the like, while the output shaft is coupled with a load to be driven. Both the load and motor are often times received on the same side of the drive housing or casing, which is typically referred to as C-flow drive. Often a mechanical or an electrical control is provided outside of the housing so as to be accessible by the user for adjusting disc spacing on the input shaft, and thereby controlling the output speed of the drive. Such drives are available in a wide variety of horsepower ratings and have numerous applications throughout a wide variety of industries.
The following U.S. patents, the disclosures of which are fully incorporated herein by reference, are examples of the above-referenced type of variable speed belt drive.
______________________________________ INVENTOR U.S. Pat. No. ISSUE DATE ______________________________________ WOYTON 4,770,065 SEP. 13, 1988 HUFF ET AL. 4,425,102 JAN. 10, 1984 MEREDITH 4,411,590 OCT. 25, 1983 HUFF ET AL. 4,384,863 MAY 24, 1983 ZIGLER 4,370,139 JAN. 25, 1983 LANDAU 3,418,863 DEC. 31, 1968 ______________________________________
It is true for virtually every type of drive, conveyor means, or other industrial piece of equipment, that routine maintenance is an absolute necessity. Because of such, it is highly desirable that routine maintenance procedures be streamlined for their efficient execution, safety, and effectiveness. In addition, the time element involved can be quite critical since drives in commercial installations are often times critical to operation of a production line or a manufacturing process.
Performance of any significant maintenance procedures on an enclosed variable speed belt drive almost always requires maintenance personnel to enter, i.e., open, the drive housing or casing. For example, two of the most common maintenance items for a variable speed belt drive involve: (1) changing the drive belt and (2) servicing the sliding disc member of the input shaft. The latter item often takes the form of replacing one or more bushings associated with the outboard or distal disc of the constant speed disc pair. In most arrangements of such a type of drive, it is typically the outboard side disc on the input shaft which slides or moves relative its paired disc, while it is the inboard disc of the disc pair received on the output shaft which is shifted during speed changing, i.e., variation of the drive ratio. Of course, wear to such bushings and/or the drive belt itself occurs simply as a result of the normal operation of a properly functioning variable speed belt drive.
Many prior art variable speed belt drives use a removable housing portion or cover as a load bearing support and/or for alignment functions. More specifically, it is typical that the housing cover provides load bearing support such as receipt of bearing means or the like for rotatably supporting an end or axial portion of a shaft, such as the output shaft.
Generally speaking, any time structural support is provided for bearings which rotatably support a shaft, such structural support also is important with respect to alignment of the bearings supported thereby, and hence, important to the rotational alignment of the supported shaft. As another general proposition, it is not desirable to have to remove support for an aligned shaft since to do so can give rise to shaft misalignment, which in many cases results in increased and excessive wear, and in worst cases can result in shaft or drive failure. Other various difficulties and drawbacks arising due to misalignment of a rotating load bearing shaft are well in industry.
In order to lesson difficulties with removing such a housing cover, some prior art devices attempt to support the output shaft and the pair of variable speed discs supported thereon by one or more bearings on a single, i.e., inner, side of the shaft. In other words, a cantilevered support arrangement is provided for the outboard or distal end of the output shaft, to eliminate housing support at such point.
However, it is widely practiced that disc shifting (i.e., spacing changes) on an output shaft of a variable speed belt drive is achieved through a spring biased mechanism or similar so that the disc spacing on the output shaft actually follows changes thereto dictated by relative movement of the drive belt in accordance with positive displacements of the constant speed discs received on the input shaft. The net effect is that installation of a drive belt generally requires a significant amount of force or effort (and sometimes involves jerking, pulling, or similar forces) in order to adequately separate the discs received on the output shaft to permit insertion of the drive belt therebetween. In other words, some degree of force is necessarily imparted to the output shaft in the region of the discs mounted thereon, as the spring biasing is overcome to separate such discs.
A cantilevered support arrangement for an output shaft does not lend itself to providing adequate rigidity during the above-referenced belt changing operations in order to avoid misalignment or other damage to the output shaft and/or other components. Such is a significant problem since replacing damaged or worn drive belts, as noted above, is one of the most frequent maintenance procedures. It is also significant from the perspective that drive belts can be readily removed, e.g., cut off, or the like, and the real problem only occurs during reinstallation, where the forces described above come into play. Of course, lateral (i.e., misaligning) forces are applied to the output shaft during its normal operations, and such could act adversely on an inadequately supported shaft.
Those of ordinary skill in the art will also understand that attempting to work with such prior art drives in such a manner as to eliminate excessive forces to force-sensitive components would only add time to an already time consuming procedure.
Another approach to minimizing removable housing cover problems is to provide a split cover arrangement, wherein two or more separately removable covers are used to cover openings at each of the respective input and output shafts, and possibly other areas. However, such an approach does not necessarily eliminate the bearing support and shaft alignment problems discussed above. Moreover, such an approach, in fact, adds to the multiplicity of separate parts often present in variable speed drives, and which must be handled during maintenance procedures. In fact, the positioning and location of certain drive installations, such as overhead, or otherwise in elevated areas, can make even the simple job of handling loose parts without loss a significant operation.
In addition, relatively large number of parts results in higher costs, particularly as the number of machined surfaces increase. Also, weight can be a factor where relatively massive, for example, cast iron, component pieces are needed in order to bolster or render adequate the rigidity of various designs. Such is frequently the case where the housing cover itself must be strong enough to be utilized for load bearing and alignment functions.
Another aspect of the foregoing problems relates to the features or components utilized in actuating speed change. It is often times in this area that the most number of parts are encountered, as well as greatest complexity of individual parts and their interconnections. The added number and complexity of the parts in such area relative other parts only adds to all of the above-referenced difficulties. Also, relative unfamiliarity of maintenance personnel when dealing with smaller parts which must fit together with precision, is again a tremendous source of time consumption and other costs.
Still further, typical prior art variable speed belt drives incorporate their various actuation features into and/or associated with the input shaft. Yet, it is the sliding or movable disc of the constant speed disc pair received on the input shaft which has bushings which are one of the most frequent wear, i.e., maintenance, problems in the variable speed drive. Accordingly, maintenance personnel are frequently called on to disassemble and reassemble actuation mechanisms associated with the input shaft simply to permit the performance of maintenance procedures to the outboard disc of the constant speed disc pair. Similarly, such outboard constant speed disc often must be removed in order to permit reinstallation of a new drive belt.